<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
  let arr=[88, 20, 10, 100, 50]
  for(let i=0;i<arr.length;i++){
    if(arr[i]===10){
      console.log(i)
    }
  }
    let arr1 = [88, 20, 30, 100, 50]
      for (let i = 0; i < arr.length; i++) {
        if (arr1[i] === 10) {
          console.log(i)
        }else{
          console.log(-1)
          break
        }
      }

  </script>
  
</body>
</html>